Yes, a sound card can be very powerful
That SW looks like a modern version of the old Spectralab program. I've got a version of it dated 2000 and it is pretty good. it is also really useful for generating multiple audio tones and also things like DTMF sequences.
However, I found it quite limited for my needs partly because I don't have a decent soundcard and also because of the fiddly necessity to calibrate it (or at least try to calibrate it) to suit the soundcard.
What I like about the 2015 is I can just stuff a signal into it and check to see if the harmonic levels are acceptable and also measure the level of the signal quite accurately.
However, I like the look of the Roland USB (192kHz 24bit) SC interface because it is portable from PC to PC so I am tempted to research/buy something like that to use with my netbook or my main PC.